NASA today announced a $1.5 billion plan to build another Mars rover based on the design of its current Curiosity rover, with the intention of sending it to the Red Planet in 2020 and perhaps storing up samples for later return to Earth.

John Grunsfeld, associate administrator for science at NASA Headquarters, insisted that the budget could handle the new commitment. "This mission concept fits within the current and projected Mars exploration budget, builds on the exciting discoveries of Curiosity, and takes advantage of a favorable launch opportunity," he said in a NASA news release.

He said the future rover would be built on the same basic design used for the Curiosity rover, which landed on Mars in August, and thus capitalize on the work that was done during Curiosity's development for its $2.5 billion Mars Science Laboratory mission. Like Curiosity, the new rover would be nuclear-powered, thanks to a spare radioisotope thermoelectric generator. Grunsfeld said the use of spare parts and existing designs would result in cost savings.

"It's the availability of the spare parts, but also the people, the engineering that went into building Curiosity that we still have," he told reporters.

Grunsfeld announced the plan during a town-hall session at the American Geophysical Union's fall meeting in San Francisco. Based on Twitter updates from the meeting, reaction was deeply mixed. "NASA town meeting audience is very quiet," Lindy Elkins-Tanton of the Carnegie Institution of Washington tweeted. "I think we are all in shock."

Projected budget cuts have cast a pall of uncertainty over future plans for interplanetary probes, but the idea of bringing samples back from Mars for study on Earth is on top of planetary scientists' priority list for the next decade. Grunsfeld told his AGU audience that the rover could have the capability to gather and store samples for later return, depending on how its science mission is defined. NASA said a science definition team would be selected to outline the mission's objectives, and that the selection of payload and scientific instruments for the mission would then be openly competed.

NASA said the mission would also help lay the groundwork for human exploration of Mars.

"The Obama administration is committed to a robust Mars exploration program," NASA Administrator Charles Bolden said in today's statement. "With this next mission, we're ensuring America remains the world leader in the exploration of the Red Planet, while taking another significant step toward sending humans there in the 2030s."

Two rovers are currently in operation on Mars — Curiosity and Opportunity. Meanwhile, three working spacecraft are orbiting the Red Planet: the European Space Agency's Mars Express as well as NASA's Mars Reconnaissance Orbiter and Mars Odyssey orbiter. Next year, NASA is due to launch the $500 million MAVEN orbiter to study Mars' upper atmosphere. In 2016, NASA plans to send a $425 million lander called InSight to delve into Mars' depths.

NASA also plans to participate in the European Space Agency's Exomars program by contributing radios for an orbiter and lander due for launch in 2016, as well as scientific apparatus for a 2018 rover. But the space agency had to trim back its commitment to Exomars early this year, in large part due to the need to cover cost overruns on the James Webb Space Telescope. The Russian Space Agency is filling the gap left by NASA's pullback.

U.S. Rep. Adam Schiff, D-Calif., who has been critical of past cutbacks in NASA's planetary science program, applauded the plan announced today.

"In its few short months on Mars, Curiosity has broadened our understanding of our planetary neighbor, and the findings announced thus far point to even greater discoveries as Curiosity continues to explore Gale Crater and Mount Sharp," Schiff said in a written statement. "An upgraded rover with additional instrumentation and capabilities is a logical next step that builds upon now-proven landing and surface operations systems."

However, Schiff said he favored launching the rover in 2018 — when the alignment of Earth and Mars is more favorable, permitting the launch of a heavier payload. "I will be working with NASA, the White House and my colleagues in Congress to see whether advancing the launch date is possible, and what it would entail," he said.